Yes, the Ca/P ratio of hydroxyapatite can be determined by X-ray diffraction (XRD). XRD is a commonly used technique for analyzing the crystal structure of a material, and can provide information about the chemical composition of the material. In the case of hydroxyapatite, XRD can be used to determine the relative proportions of calcium and phosphorus in the material, and hence the Ca/P ratio.

SEM-EDS (scanning electron microscopy-energy dispersive spectroscopy) is another technique that can be used to determine the Ca/P ratio of hydroxyapatite. SEM-EDS involves using a scanning electron microscope (SEM) to obtain high-resolution images of the material, and an energy dispersive spectrometer (EDS) to analyze the elemental composition of the material. By analyzing the relative amounts of calcium and phosphorus in the hydroxyapatite using SEM-EDS, it is possible to determine the Ca/P ratio of the material.

In general, both XRD and SEM-EDS are useful techniques for determining the Ca/P ratio of hydroxyapatite, and can provide valuable information about the material's properties and behavior.

For XRD:

Article Determination of the Ca/P Ratio in Calcium-Deficient Hydroxy...

https://www.researchgate.net/post/Can_Ca_P_ratio_be_determined_by_XRD

For EDS it's better to quantify using standards. As a simple standard you can use stoichiometric hydroxyapatite. I believe EDS method is pretty simple, if less precise. But you need bulk material thicker than 3-5 microns.

I think that EDS is a more direct technique to determine the Ca/P ratio. In fact the element amount is provided as mol or wt% allowing to directly determine their ratio. The XRD analysis is a little bit expensive in time to reach the same information.

The EDAX is not a recommended method for hydroxyapatite since gold coating in SEM makes negative results for Ca in HA structure.

Dear Shima Tavakol , EDS is a recommended method, since gold coating is not mandatory.

Dear Vladimir Dusevich, since the most researchers coat the samples using gold for SEM and as the same time analysis the EDAX, therefore it should be considered that they do not coated the samples if they want to perform EDS for Ca/P components.

Recommended coating for EDS - carbon. But even proper (means thin) gold coating would not significantly alter Ca/P ratio.